IPAC2014 - Classification: 07 Accelerator Technology Main Systems / T06 Room Temperature RF

Paper	Title	Page
MOOCA01	High Power Test Results of the SPARC C-Band Accelerating Structures	39
	D. Alesini, M. Bellaveglia, M.E. Biagini, R. Boni, P. Chimenti, R. Clementi, G. Di Pirro, R. D. Di Raddo, M. Ferrario, A. Gallo, V.L. Lollo INFN/LNF, Frascati (Roma), Italy M. Brönnimann, R. Kalt, T. Schilcher PSI, Villigen PSI, Switzerland L. Ficcadenti INFN-Roma, Roma, Italy L. Palumbo URLS, Rome, Italy
	The energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. In the paper we present the results of the low and high power RF tests on the two final fabricated structures that shown the feasibility of the operation at accelerating gradients larger than 35 MV/m.
	Slides MOOCA01 [6.242 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOOCA01
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MOOCA02	RF Design and Operation of a Modular Cavity for Muon Ionization Cooling R&D	42
	Y. Torun IIT, Chicago, Illinois, USA D.L. Bowring, M.A. Palmer, K. Yonehara Fermilab, Batavia, Illinois, USA
	Funding: Supported by the US Department of Energy Office of Science through the Muon Accelerator Program. Ionization cooling channel designs call for the operation of high-gradient, normal-conducting RF cavities in multi-Tesla solenoidal magnetic fields. However, strong magnetic fields have been shown in some cases to limit the maximum achievable gradient in RF cavities. This gradient limit is characterized by RF breakdown and damage to the cavity surface. To study this issue, we have developed an experimental program at Fermilab's MuCool Test Area (MTA) based on a modular pillbox cavity operating at 805 MHz. The modular cavity design allows for the evaluation of different cavity geometries and materials – such as beryllium – which may ameliorate or circumvent RF breakdown triggers. We present a summary of recent results and plans for the future of the MTA normal conducting RF cavity program.
	Slides MOOCA02 [32.552 MB]
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THPRO046	100 MHz RF System as an Alternative for the Iranian Light Source Facility	2968
	S. Pirani, H. Ghasem, M. Moradi, Kh.S. Sarhadi ILSF, Tehran, Iran
	The Iranian Light Source Facility (ILSF) RF system was conceptually designed based on ILSF requirements for a 3GeV storage ring and 400 mA beam current at 500 MHz RF frequency. The development of HOM damped cavity with simpler structure at 100MHz and advantages of reducing frequency as investigated at MAX Lab, provided an alternative of 100MHz RF system to be explored for ILSF. RF frequency change and its effects on the beam and machine parameters as well as the availability and cost of RF system components have been studied for ILSF. The conceptual design of a 100MHz RF system and the comparison between 500 MHz and 100 MHz RF frequencies are presented in this report. This paper, furthermore, provides details about the 100MHz RF cavity designed by ILSF RF group based on MAX Lab cavity.
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THPRO078	Time-dependent Behaviour of Gas Ejected from an Accelerating Structure after a Discharge	3062
	V.G. Ziemann Uppsala University, Uppsala, Sweden
	Funding: This work is supported by the 7th European Framework program EuCARD under grant number 227579. A discharge or RF-breakdown event in a CLIC acceleration structure causes the localized release of gas molecules inside a thin conduction limited system with distributed pumping. We discuss the transient behavior of such a system in the molecular flow regime that allows an analytical solution with the help of Greens functions. They describe the temporal evolution of the gas density and the gas flow ejected from the ends of thin pipes of finite length. Distributed pumping, for example through the HOM damping slits is taken into account.
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THPME054	RF Cavity Design Aspects for a Helical Muon Beam Cooling Channel	3352
	F. Marhauser, G. Flanagan, R.P. Johnson, S.A. Kahn Muons, Inc, Illinois, USA K. Yonehara Fermilab, Batavia, Illinois, USA
	Funding: Work supported under U.S. DOE Grant Application Number DE-SC0006266 A Helical Cooling Channel (HCC) promises efficient six-dimensional ionization cooling of muon beams by utilizing high-pressurized gas as a continuous absorber within a magnetic channel embedding RF cavities. The progress on cavity design, tailored for such a cooling channel, is discussed.
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THPRI031	Design and Commissioning of S-Band RF Station for AREAL Test Facility	3834
	A. Vardanyan, H. Avdishyan, H. Davtyan, B. Grigoryan, L.H. Hakobyan, H. Poladyan CANDLE SRI, Yerevan, Armenia
	The RF station has been designed and constructed for AREAL Linac. The constructional features and commissioning results of RF system are presented. The whole RF system is designed to work at 3GHz frequency. The linac includes an electron gun for 0.5-8 ps electron bunch production with 1-10 Hz repetition rate. For linac RF control system a Libera LLRF stabilization system is used. An important feature of the presented system is a high level synchronization of amplitude-phase characteristics which provide the required accuracy for particle acceleration and bunch formation.
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THPRI032	Study of a RF Gun with a Thermoionic Cathode	3837
	A.S. Setty, A.S. Chauchat, D. Fasse, D. Jousse, P. Sirot Thales Communications & Security (TCS), Gennevilliers Cedex, France
	The low energy part of our pre injectors* is made up of a 90 kV DC thermoionic triode gun, followed by a 500 MHz sub harmonic prebuncher and a 3 GHz prebuncher. These two cavities are respectively fed with 500 W, a modulation of ± 25 kV, and 90 W corresponding to a ± 10 kV. The gun grid is modulated within a 500 MHz signal. The initial 1 ns phase extension at the gun level is reduced, at the buncher entry, to 40 ps for 75% of the gun current. This study proposes to replace the gun and the two cavities by a RF gun integrated in a modulated cavity at 200 MHz followed by a drift in order to bunch the beam. This study will compare the beam dynamics simulations for these two cases. *A. Setty et al, "Design and Construction of Turnkey Linacs as Injectors for Light Sources", Proceedings IPAC 2012, USA, Louisiana, May 2012.
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THPRI033	Design of New Buncher Cavity for Relativistic Electron Gun for Atomic Exploration – REGAE	3840
	M. Fakhari, H. Delsim-Hashemi, K. Flöttmann, M. Hüning, S. Pfeiffer, H. Schlarb DESY, Hamburg, Germany J. Roßbach Uni HH, Hamburg, Germany
	The Relativistic Electron Gun for Atomic Exploration, REGAE, is a small electron accelerator build and operated at DESY. Its main application is to provide high quality electron bunches for time resolved diffraction experiments. The RF system of REGAE contains different parts such as low level RF, preamplifier, modulator, phase shifter, and cavities. A photocathode gun cavity to produce the electrons and a buncher cavity to compress the electron bunches in the following drift tube. Since the difference between the operating mode of the existing buncher and its adjacent mode is too small, the input power excites the other modes in addition to the operating mode which affects the beam parameters. A new buncher cavity is designed in order to improve the mode separation. Furthermore the whole cavity is modeled by a circuit which can be useful especially during the tuning process. Beam dynamics simulations have been performed in order to compare the new designed cavity with the old one which declare that the effects of the adjacent modes on the beam parameters are decreased.
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THPRI035	Design and Simulation of Side Coupled Six MeV Linac for X-Ray Cargo Inspection	3844
	S. Ahmadiannamin, F. AbbasiDavani, R. Ghaderi, F. Ghasemi sbu, Tehran, Iran M. Lamehi Rashti IPM, Tehran, Iran S. Zarei Nuclear Science and Technology Research, InstituteRadiation Application School, Tehran, Iran
	Using in X-ray cargo inspection is one of most applications of linear accelerators. This paper represents design and simulation of Side Coupled Six MeV cavity. The electromagnetic simulation of structure was carried out in the SUPERFISH and CST Microwave studio. 2.3 MW input power is considered according to MG5193 magnetron. The coupling coefficient is calculated equal to 3% for stabilization of accelerator operation against environmental and mechanical errors effects.
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THPRI038	Simulation Study of Electron Gun for Six MeV Linac for X-Ray Cargo Inspection	3847
	S. Ahmadiannamin, F. AbbasiDavani, R. Ghaderi, F. Ghasemi sbu, Tehran, Iran M. Lamehi Rashti IPM, Tehran, Iran S. Zarei Nuclear Science and Technology Research, InstituteRadiation Application School, Tehran, Iran
	Electron guns are designed in different models. Output beam quality and efficiency of the linear accelerator for each application depends on choosing the suitable model of electron gun. The most common types are diode and triode electron guns. Simulation Study of diode electron gun of Six MeV Linac for X-Ray Cargo Inspection represented in this article. Vaughan analytical method was used to obtain the initial dimensions. In final stage, CST Particle Studio software used to obtain the dimensional details.
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THPRI041	Twenty Years of Operation of the Elettra RF System	3853
	C. P. Pasotti, M. Bocciai, P. Pittana, M. Rinaldi Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	Six thousand hours per year is the typical running scheduled time of the user-dedicated Elettra facility and twenty years is a significant amount of operating hours for the RF system. Failure and weak points of the installed equipment is discussed as well as the up-time statistic. The effectiveness of the predictive versus the extraordinary maintenance is presented. The gained operational experience has allowed the planning of the priorities to refit the installed components within a reasonable budget, in compliance with the user-operation time schedule and following the technical need of upgrading to improve the RF system performance.
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THPRI042	Design and RF Test of Damped C-Band Accelerating Structures for the ELI-NP Linac	3856
	D. Alesini, S. Bini, R. D. Di Raddo, V.L. Lollo, L. Pellegrino INFN/LNF, Frascati (Roma), Italy L. Ficcadenti, V. Pettinacci INFN-Roma, Roma, Italy L. Palumbo URLS, Rome, Italy L. Serafini Istituto Nazionale di Fisica Nucleare, Milano, Italy
	The linac energy booster of the European ELI-NP proposal foresees the use of 12 traveling wave C-Band structures, 1.8 m long with a field phase advance per cell of 2pi/3 and a repetition rate of 100 Hz. Because of the multi-bunch operation, the structures have been designed with a damping of the HOM dipoles modes in order to avoid beam break-up (BBU). They are quasi-constant gradient structures with symmetric inputs couplers and a strong damping of the HOM in each cell. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce their cost. In the paper we shortly review the whole design criteria and we illustrate the low and high power RF test results on prototypes that shown the feasibility of the structure realization and the effectiveness of the HOM damping.
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THPRI043	Thermal-mechanical Analysis of the RF Structures for the ELI-NP Proposal	3860
	V. Pettinacci INFN-Roma, Roma, Italy D. Alesini, L. Pellegrino INFN/LNF, Frascati (Roma), Italy L. Palumbo URLS, Rome, Italy
	The room temperature RF structures in the ELI-NP Linac will operate in multi-bunch with high repetition rate (100 Hz). For these reasons they are subject to some kW of power dissipated on the internal cavities surfaces. The resulting thermal deformation of the cavities shapes could imply variations in their electromagnetic fields. To limit these effects and optimize the cooling design, a fully coupled ElectroMagnetic- Thermal-Mechanical analysis has been performed on the S-Band Radiofrequency Gun and on the C-Band multi-cell structures. In the paper the study done in Ansys Workbench with HFSS and Ansys Mechanical is reviewed
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THPRI044	Vacuum Waveguide System for SPring-8 Linac Injector Section	3863
	T. Taniuchi, H. Dewa, H. Hanaki, T. Kobayashi, T. Magome, A. Mizuno, S. Suzuki, K. Yanagida JASRI/SPring-8, Hyogo-ken, Japan
	An SF6 waveguide system for the injector section of SPring-8 linac has been replaced in a vacuum waveguide system including a newly developed vacuum circulator and an isolator. This paper describes developed RF components, a waveguide configuration and an RF conditioning of the system.
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THPRI045	Development of a 1.3-GHz Buncher Cavity for the Compact ERL	3866
	T. Takahashi, Y. Honda, T. Miura, T. Miyajima, H. Sakai, S. Sakanaka, K. Shinoe, T. Uchiyama, K. Umemori, M. Yamamoto KEK, Ibaraki, Japan
	In a high-brightness injector of the Compact ERL (cERL), a 1.3-GHz buncher cavity is used to compress the electron bunches which are produced at a 500-kV photocathode DC electron gun. An rf voltage required is about 130 kV. To elongate the lifetime of the photocathode of the DC gun which is located beside the buncher cavity, an extremely-low pressure of about 10^-9 Pa is required in the buncher cavity under operating conditions. In order to achieve such low pressures, we have developed a normal-conducting cavity which included several measures to reduce the outgas from the cavity components, together with careful rf designs to avoid any problems due to multipactor discharges or to other problems. With the developed cavity, we achieved a vacuum pressure of about 2·10^-9 Pa under rf operations at an rf voltage of about 100 kV. The buncher cavity was installed in the cERL, and it worked very well; we could demonstrate to compress the bunch length from 10 ps (FWHM) to 0.5 ps (rms) using the buncher cavity.
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THPRI046	Air-cooled Magnetic Alloy Cavity for J-PARC Doubled Rep.-rate Scenario	3869
	C. Ohmori, K. Hara, K. Hasegawa, K. Takata, M. Toda, M. Yoshii KEK, Ibaraki, Japan M. Nomura, A. Schnase, T. Shimada, F. Tamura, M. Yamamoto JAEA/J-PARC, Tokai-mura, Japan
	The upgrade project of the J-PARC MR (Main Ring) is in progress to deliver the beam power of 750 kW based on doubled repetition-rate scenario. The present RF section will be occupied by 9 sets of new magnetic alloy, FT3L, cavity using the direct water cooling scheme. The direct water cooling requires dedicated high-quality cooling water. These cavities will be used for the fundamental RF for acceleration. The second harmonic RF is necessary to increase the bunch length. This allows to enlarge the beam current, and to relax the space charge effects during the injection. Thanks to the high impedance FT3L, the power loss in the second harmonic RF system becomes moderate. The air cooled cavity is designed to fit in any space in the MR where the dedicated water is not available. This paper reports the design of the second RF system, technical issues to produce the magnetic alloy cores to fit the air cooling, and construction of the system.
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THPRI047	Large-aperture Travelling-wave Accelerator Structure for Positron Capture of SuperKEKB Injector Linac	3872
	S. Matsumoto, T. Higo, K. Kakihara, T. Kamitani, M. Tanaka KEK, Ibaraki, Japan
	Comparing to the previous KEKB, the four-times higher charge of 4 nC per bunch is required for the injector linac of SuperKEKB. Not only a flux concentrator will be introduced but also the physical aperture of the downstream six 2m-long accelerator structures was increased as large as 30mm in diameter. We call these structures as LAS, “Large Aperture S-band” structure. The resultant higher RF group velocity of about 3% makes the acceleration gradient lower. In the nominal acceleration system, a 40MW klystron with SLED feeds four 2m-long accelerator structures producing 20MV/m acceleration field. The acceleration gradient higher than 14 MV/m is required for the very first two LAS structures to suppress the satellite bunches. This gradient is obtained by feeding only two LAS structures. Initially, ten LAS structures were installed and the RF processing has partly started. In the present paper, we firstly describe the acceleration system design and then present the processing characteristics through the RF processing without beam and with beam.
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THPRI048	Design of an Accelerating Tube for a Standing-wave Accelerator based on Genetic Algorithm’s Optimal Calculation	3875
SUSPSNE090	use link to see paper's listing under its alternate paper code
	Z.X. Tang USTC, Hefei, Anhui, People's Republic of China Y.J. Pei USTC/NSRL, Hefei, Anhui, People's Republic of China
	A compact medical standing-wave (SW) electron accelerating tube has been designed that operating frequency is 2998MHz, operating mode is π/2, final energy is 6MeV and beam current is 100mA based on genetic algorithm (GA)’s optimal calculation. It employed a bi-periodic structure with nose cone shape. We performed the simulation experiment which proved that GA was feasible and gave a set of geometric parameter with higher shunt impedance. We performed tuning of the whole tube by CST MICROWAVE STUDIO and SUPERFISH and calculation of beam dynamics by ASTRA and Parmela in this paper. The total length of the tube is less than 300mm.
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THPRI049	Engineering Design of the RF Input Couplers for C-ADS RFQ	3878
	L.P. Sun, Y. He, A. Shi, C. Zhang, Z.L. Zhang IMP, Lanzhou, People's Republic of China
	A new coupler with the special ceramic window has been developed at IMP, CAS (Institute of Modern Physics, Chinese Academy of Sciences), operating at 30 kW/162.5 MHz in CW mode for an one-meter prototype cavity, which can provide all kinds of experiences to the real four-meter cavity including EM simulation, power conditioning, cooling consideration and so on. Now, the beam experiments on prototype cavity have been completed and the results show the simulation and the measurements of coupler were in the good agreement. The special bowl-type ceramic window can promote S parameter and reduce sparking risk for beam commissioning stably. A detailed electromagnetic design and measured results of the coupler will be presented in the paper.
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THPRI050	Calculation and Design of the Re-buncher Cavities for the LIPAc Deuteron Accelerator	3881
	D. Gavela, I. Podadera, F. Toral CIEMAT, Madrid, Spain
	Funding: This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project AIC-A-2011-0654 Two re-buncher cavities are necessary for the LIPAc (Linear IFMIF Prototype Accelerator), presently being built at Rokkasho (Japan). They are placed at the Medium Energy Beam Transport (MEBT) line to longitudinally focus a 5 MeV CW deuteron beam. Due to the strong space charge and the compactness of the beamline, the cavity has several space restrictions. In order to minimize the power loss, an IH-type cavity with 5 gaps was selected. It provides an effective voltage of 350 kV at 175 MHz with a power loss of 6.6 kW. First, electromagnetic calculations have been done with HFSS to compute the resonant frequency, the S-parameters, the electric and magnetic field maps, the power losses and the proper geometry for a magnetic input coupler and a pickup probe. Then, a mechanical Ansys model has been used to analyze the stresses and deformations due to vacuum, the cooling circuit and the temperature distribution, taking into account the power losses imported from the electromagnetic model. Finally, the fluid dynamics in the cooling circuits of the stems has been carefully studied.
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THPRI051	Fabrication and Tests of the Re-buncher Cavities for the LIPAc Deuteron Accelerator	3884
	D. Gavela, P. Abramian, J. Calero, A. Guirao, J.L. Gutiérrez, E. Molina Marinas, I. Podadera, L. Sánchez, F. Toral CIEMAT, Madrid, Spain
	Funding: This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project AIC-A-2011-0654 Two re-buncher cavities will be installed at the Medium Energy Beam Transport (MEBT) of the LIPAc accelerator, presently being built at Rokkasho (Japan). They are IH-type cavities with 5 gaps and will provide an effective voltage of 350 kV at 175 MHz. The cavity consists of a cylindrical main body and two endplates in stainless steel with an internal copper coating. The stems and drift tubes are machined from bulk OFE copper. The fabrication techniques for the cooling pipes, the input coupler and the pick-up are presented. Material choices and fabrication process are discussed. The first re-buncher is already fabricated. RF low power tests have been made to measure resonant frequency, S-parameters and Q-factor before and after the copper plating. The electric field map has also been measured with the bead-pull method.
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THPRI052	Design, Fabrication and Tests of the Second Prototype of the Double-Length CLIC PETS	3887
	L. Sánchez, J. Calero, D. Gavela, J.L. Gutiérrez, F. Toral CIEMAT, Madrid, Spain D. Gudkov, G. Riddone CERN, Geneva, Switzerland
	Funding: This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project FPA2010-21456-C02-02 The future collider CLIC is based on a two-beam acceleration scheme, where the drive beam provides to the main beam the RF power through the Power Extraction and Transfer Structures (PETS). The technical feasibility of some components is currently being proved at the CLIC Experimental Area (CLEX). Two double- length CLIC PETS will be installed in CLEX to validate their performance with beam. The first prototype was produced and validated in 2012. This paper is focused on the engineering design, fabrication and validation of the second prototype. Taking into account the results of the first prototype, some modifications have been included in the design to ease fabrication and assembly. The fabrication techniques are very similar to the ones used for the first prototype. Mechanical measurements on single parts and different assembly stages will be reported. The industrialization feasibility will be also analyzed. Finally, several tests such as vacuum tightness and RF measurements with low power have been realized to validate the device. These results are compared with the first prototype ones.
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THPRI053	Ferrite Material Characterization in a Static Bias Field for the Design of a Tunable Cavity	3890
SUSPSNE088	use link to see paper's listing under its alternate paper code
	J. Eberhardt, F. Caspers, C. Vollinger CERN, Geneva, Switzerland
	During the development of ferrite-loaded accelerating cavities, the electromagnetic properties of the dispersive ferrite material need to be known. We describe a coaxial short-circuit measurement technique to measure the complex permeability of toroidal-shaped samples (127mm outer and 70mm inner diameter) that are exposed to an external magnetic bias field. The external magnetic bias field is applied perpendicular to the RF magnetic field. With this method it is possible to characterize the frequency dependence of the permeability for a frequency range of 1-100MHz. The dependence of the permeability on the external magnetic bias is presented for the ferrite G-510 from Trans-Tech Inc. and the material characterization is shown in the same frequency range. The measurement results are verified by simulations of the measurement set-up.
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THPRI054	Permittivity and Permeability Measurement Methods for Particle Accelerator Related Materials	3893
	C. Vollinger, F. Caspers, E. Jensen CERN, Geneva, Switzerland
	For the special requirements related to particle accelerators, knowledge of the different material parameters of dielectrics and other materials are needed in order to carry out simulations during the design process of accelerator components. This includes also properties of magnetically biased ferrites of which usually little information is available about material characteristics, especially in magnetic bias fields. Several methods of measurement are discussed and compared of which some require delicate sample preparation whereas others can work with unmodified material shapes that makes those methods also suited for acceptance checks on incoming materials delivered by industry. Applications include characterization of different materials, as absorbers in which dielectric losses play an increasing role, as well as low frequency measurements on ferrites that are used for tunable cavities. We present results obtained from both broadband and resonant measurements on different materials determined in the same sample holder. Where possible, the results were confirmed with alternative methods.
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THPRI055	The New 118 MHz Normal Conducting RF Cavity for SIAM Photon Source at SLRI	3896
	N. Juntong, S. Krainara SLRI, Nakhon Ratchasima, Thailand
	The Siam Photon Source (SPS) is the 1.2 GeV second generation light source in Thailand. It is managed by the Synchrotron Light Research Institute (SLRI). The institute is located inside the campus of Suranaree University of Technology (SUT), which is approximately 20 km from the city of Nakhon Ratchasima (or normally called Korat). Korat is 250 km north-east of Bangkok. Two insertion devices (IDs) have been installed in the SPS storage ring during June to August 2013. These IDs require additional electrical field energy from RF cavity to compensate electron energy loss in the storage ring. The existing RF cavity has been pushed to its maximum capability and the new RF cavity is in the procurement process. The design and study of the new RF cavity will be presented. Electromagnetic fields of the cavity are studied together with the effects to electron beam instabilities.
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THPRI056	A New Debunching Cavity for the ISIS H⁻ Injector	3899
	B.S. Drumm, A.P. Letchford, R.E. Williamson STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom M. Keelan STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
	The energy range of the ISIS 70MeV H⁻ injected beam is reduced using an RF debunching cavity. The existing cavity consists of a mild steel vacuum vessel containing a water-cooled copper shell into which RF power is fed. The unit is made up of components designed for the 50 MeV Proton Linear Accelerator (PLA) which used to occupy the Rutherford Appleton Laboratory (RAL) site between 1957 and 1969. The component drawings date back to the late 1960s. Due to its age, complexity and a lack of spares, there is a need for a modern solution. This paper documents the development of a new debunching cavity for the ISIS neutron source.
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THPRI058	RF Delivery System for FETS	3902
	S.M.H. Alsari, M. Aslaninejad, J.K. Pozimski, P. Savage Imperial College of Science and Technology, Department of Physics, London, United Kingdom M. Dudman, A.P. Letchford STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
	The Front End Test Stand (FETS) is an experiment based at the Rutherford Appleton Laboratory (RAL) in the UK. In this experiment, the first stages necessary to produce a very high quality, chopped H⁻ ion beam as required for the next generation of high power proton accelerators (HPPAs) are designed, built and tested. HPPAs with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, accelerator driven sub-critical systems, waste transmuters and tritium production facilities. An RF system outline, circulator high power tests, RF amplifiers tests, waveguide run with shielding and couplers design are presented and discussed in this paper. Experimental measurements of the system’s circulator and RF Amplifiers high power test will be presented as part of the system testing results.
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THPRI059	Field Emission Study of RF cavity in Static Magnetic Field	3905
	T.H. Luo, D. Li LBNL, Berkeley, California, USA W. Gai ANL, Argonne, Illinois, USA J.H. Shao TUB, Beijing, People's Republic of China
	The RF cavity performance in solenoid magnetic field is crucial for the muon ionization cooling. Previous experiments have shown that the strong external magnetic field can significantly lower the maximum achievable RF voltage in the cavity. The mechanism of this performance degradation has been studied both analytically and experimentally, but so far no conclusive cause has been determined yet. In this paper, we propose an experiment to study the effect of a static B field on the field emission in the RF cavity, which hasn't been investigated before, and which can contribute to the cavity performance degradation in the solenoid field.
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THPRI061	Perpendicular Biased Ferrite Tuned Cavities for the Fermilab Booster	3911
	G.V. Romanov, M.H. Awida, T.N. Khabiboulline, W. Pellico, C.-Y. Tan, I. Terechkine, V.P. Yakovlev, R.M. Zwaska Fermilab, Batavia, Illinois, USA
	The aging Fermilab Booster RF system needs an upgrade to support future experimental program. The important feature of the upgrade is substantial enhancement of the requirements for the accelerating cavities. The new requirements include enlargement of the cavity beam pipe aperture, increase of the cavity voltage and increase in the repetition rate. The modification of the present traditional parallel biased ferrite cavities is rather challenging. An alternative to rebuilding the present Fermilab Booster RF cavities is to design and construct new perpendicular biased RF cavities, which potentially offer a number of advantages. An evaluation and a preliminary design of the perpendicular biased ferrite tuned cavities for the Fermilab Booster upgrade is described in the paper. Also it is desirable for better Booster performance to improve the capture of beam in the Booster during injection and at the start of the ramp. One possible way to do that is to flatten the bucket by introducing second harmonic cavities into the Booster. This paper also looks into the option of using perpendicularly biased ferrite tuners for the second harmonic cavities.
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THPRI064	Plasma Chemistry in a High Pressure Gas Filled RF Test Cell for use in a Muon Cooling Channel	3917
	B.T. Freemire, Y. Torun IIT, Chicago, Illinois, USA M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, T.A. Schwarz, A.V. Tollestrup, Y. Torun, K. Yonehara Fermilab, Batavia, Illinois, USA R.P. Johnson Muons, Inc, Illinois, USA
	Filling an RF cavity with a high pressure gas prevents breakdown when the cavity is placed in a multi-Tesla external magnetic field. A beam of particles traversing the cavity, be it muons or protons, ionizes the gas, creating an electron-ion plasma which absorbs energy from the cavity. In order to understand the nature of this plasma loading, a variety of gas species, gas pressures, dopants, and cavity electric fields were investigated. Plasma induced energy loss, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times were measured. The results for hydrogen, deuterium, helium, and nitrogen, doped with dry air will be presented.
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THPRI066	Design of a 1.3 GHz Two-cell Buncher for APEX	3924
	H.J. Qian, K.M. Baptiste, J.A. Doyle, D. Filippetto, S. Kwiatkowski, C. F. Papadopoulos, D. Patino, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA
	Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The design of a 1.3 GHz buncher cavity for the APEX project, a MHz repetition rate high-brightness photoinjector, is presented. The buncher cavity operates at 240 kV in CW mode, and it compresses the 750 keV beam from APEX gun through ballistic compression. Compared with a single cell design, a two-cell cavity doubles the shunt impedance to 7.8 MΩ, which greatly relaxes the requirements for both RF amplifier and cavity cooling. Coupler design, multipacting analysis, HOM analysis and thermal analysis will be presented in this paper.
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THPRI070	Tuner System Simulation and Tests for the 201-MHz MICE Cavity	3927
	L. Somaschini INFN-Pisa, Pisa, Italy A.J. DeMello, A.R. Lambert, S.P. Virostek LBNL, Berkeley, California, USA J.H. Gaynier, R.J. Pasquinelli, D.W. Peterson, R.P. Schultz Fermilab, Batavia, Illinois, USA Y. Torun Illinois Institute of Technology, Chicago, Illlinois, USA
	Funding: Supported by the US Department of Energy Office of Science through the Muon Accelerator Program. The frequency of MICE cavities is controlled by pneumatic tuners as their operation is impervious to large magnetic fields. The mechanical and RF transfer functions of the tuner were simulated in ANSYS. The first of these tuning systems was assembled and tested at Fermilab. The mechanical response and the RF tuning transfer function have been measured and compared with simulation results. Finally the failure of different actuators has been simulated and tested to predict the operational limits of the tuner.
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THPRI073	Achieving Higher Energies via Passively Driven X-band Structures	3933
SUSPSNE089	use link to see paper's listing under its alternate paper code
	T. Sipahi, S. Biedron, S.V. Milton CSU, Fort Collins, Colorado, USA
	Due to their higher intrinsic shunt impedance X-band accelerating structures significant gradients with relatively modest input powers, and this can lead to more compact particle accelerators. At the Colorado State University Accelerator Laboratory (CSUAL) we would like to adapt this technology to our 1.3 GHz L-band accelerator system using a passively driven 11.7 GHz traveling wave X-band configuration that capitalizes on the high shunt impedances achievable in X-band accelerating structures in order to increase our overall beam energy in a manner that does not require investment in an expensive, custom, high-power X-band klystron system. Here we provide the design details of the X-band structures that will allow us to achieve our goal of reaching the maximum practical net potential across the X-band accelerating structure while driven solely by the beam from the L-band system.
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THPRI075	S-Band Structure Study for the MaRIE Project	3940
	Z. Li, C. Adolphsen, M.V. Fazio, S.G. Tantawi, L. Xiao SLAC, Menlo Park, California, USA
	Funding: Work was supported by the US Department of Energy through the LANL/LDRD Program. The Matter-Radiation Interactions in Extremes (MaRIE) facility proposed at LANL utilizes a 20-GeV electron linac to drive a 50-keV XFEL. Experimental requirements drive a need for multiple photon bunches over time durations of about 10 microsecond produced by a bunch train of interleaving 0.1 nC very low-emittance bunches with 2-nC electron bunches. The linac is required not only to provide high gradient and high efficient acceleration, but also a controlled wakefield profile to maintain the beam quality. In this paper, we explore the feasibility of using the S-Band technology to meet such acceleration requirements. We will present the design optimization and comparison of S-Band structures based on different design considerations.
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THPRI076	Laser Triggered RF Breakdown Study Using an S-band Photocathode Gun	3943
	J.H. Shao, W. Gai ANL, Argonne, Illinois, USA H.B. Chen, Y.-C. Du, W.-H. Huang, J. Shi, C.-X. Tang, L.X. Yan TUB, Beijing, People's Republic of China C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA F.Y. Wang SLAC, Menlo Park, California, USA
	A laser triggered RF breakdown experiment was carried out with an S-band photocathode gun at Tsinghua University for attempting understanding of the RF breakdown processes. By systematic measurement of the time dependence of the breakdown current at the gun exit and the stored RF energy in the cavity, one might gain insight into the time evolution of RF breakdown physics. A correlation of the stored energy and field emission current has been analysed with an equivalent circuit model. Experimental details and analysis methods are reported.
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THPRI077	Electric Field Enhancement Study using an L-band Photocathode Gun	3946
	J.H. Shao, W. Gai ANL, Argonne, Illinois, USA H.B. Chen, J. Shi TUB, Beijing, People's Republic of China C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA F.Y. Wang, L. Xiao SLAC, Menlo Park, California, USA
	RF breakdown in high gradient accelerating structures is a fundamental problem that is still needed better understanding. Past studies have indicated that field emission, which is usually represented by electric field enhancement (i.e. β) produced from the Fowler-Nordheim plot, is strongly coupled to the breakdown problem. A controlled surface study using a high gradient L-band RF gun is being carried out. With a flat cathode, the maximum electric field on the surface reached 10³ MV/m. And electric field as high as 565 MV/m on the surface was achieved by a pin-shaped cathode. The field enhancement factor was measured at different surface field during the conditioning process. Initial results of the study are presented in this paper.
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THPRI078	Experimental Study of Surface RF Magnetic Field Enhancement Caused by Closely Spaced Protrusions	3949
	F.Y. Wang, C. Adolphsen, J.P. Eichner, C.D. Nantista, L. Xiao SLAC, Menlo Park, California, USA
	The RF magnetic field enhancement between two closely spaced protrusions on a metallic surface has been studied theoretically. It is found that a large enhancement occurs when the field is perpendicular to the gap between the protrusions. This mechanism could help explain the melting that has been observed on cavity surfaces subjected to pulsed heating that would nominally be well below the melting temperature of the surface material. To test this possibility, an experiment was carried out in which a pair of copper “pins” was attached to the base plate of an X-band cavity normally used to study pulsed heating. Melting was observed between the pins when the predicted peak temperature was near or exceeded the copper melting temperature.
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THPRI080	The New Design for Capture Cavity of CEBAF	3955
	S. Wang, J. Guo, R.A. Rimmer, H. Wang JLab, Newport News, Virginia, USA
	In CEBAF, the electron beam from the injector must be sufficiently relativistic to match a 1 GeV recirculated beam in the first linac. The electron beam is produced with a ~130 keV electron gun, then accelerated by a room temperature, graded-beta standing wave linac, capture section, from 130 keV to 510 keV before enters two 5-cell superconducting RF cavities for further acceleration. Present capture cavity is a 5-cell side-coupled cavity. We designed a new slot-coupled cavity which has lower power consumption and simpler structure.
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Paper

Title

Page

High Power Test Results of the SPARC C-Band Accelerating Structures

39

D. Alesini, M. Bellaveglia, M.E. Biagini, R. Boni, P. Chimenti, R. Clementi, G. Di Pirro, R. D. Di Raddo, M. Ferrario, A. Gallo, V.L. Lollo
INFN/LNF, Frascati (Roma), Italy
M. Brönnimann, R. Kalt, T. Schilcher
PSI, Villigen PSI, Switzerland
L. Ficcadenti
INFN-Roma, Roma, Italy
L. Palumbo
URLS, Rome, Italy

The energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. In the paper we present the results of the low and high power RF tests on the two final fabricated structures that shown the feasibility of the operation at accelerating gradients larger than 35 MV/m.

Slides MOOCA01 [6.242 MB]

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MOOCA02

RF Design and Operation of a Modular Cavity for Muon Ionization Cooling R&D

42

Y. Torun
IIT, Chicago, Illinois, USA
D.L. Bowring, M.A. Palmer, K. Yonehara
Fermilab, Batavia, Illinois, USA

Funding: Supported by the US Department of Energy Office of Science through the Muon Accelerator Program.
Ionization cooling channel designs call for the operation of high-gradient, normal-conducting RF cavities in multi-Tesla solenoidal magnetic fields. However, strong magnetic fields have been shown in some cases to limit the maximum achievable gradient in RF cavities. This gradient limit is characterized by RF breakdown and damage to the cavity surface. To study this issue, we have developed an experimental program at Fermilab's MuCool Test Area (MTA) based on a modular pillbox cavity operating at 805 MHz. The modular cavity design allows for the evaluation of different cavity geometries and materials – such as beryllium – which may ameliorate or circumvent RF breakdown triggers. We present a summary of recent results and plans for the future of the MTA normal conducting RF cavity program.

Slides MOOCA02 [32.552 MB]

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THPRO046

100 MHz RF System as an Alternative for the Iranian Light Source Facility

2968

S. Pirani, H. Ghasem, M. Moradi, Kh.S. Sarhadi
ILSF, Tehran, Iran

The Iranian Light Source Facility (ILSF) RF system was conceptually designed based on ILSF requirements for a 3GeV storage ring and 400 mA beam current at 500 MHz RF frequency. The development of HOM damped cavity with simpler structure at 100MHz and advantages of reducing frequency as investigated at MAX Lab, provided an alternative of 100MHz RF system to be explored for ILSF. RF frequency change and its effects on the beam and machine parameters as well as the availability and cost of RF system components have been studied for ILSF. The conceptual design of a 100MHz RF system and the comparison between 500 MHz and 100 MHz RF frequencies are presented in this report. This paper, furthermore, provides details about the 100MHz RF cavity designed by ILSF RF group based on MAX Lab cavity.

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THPRO078

Time-dependent Behaviour of Gas Ejected from an Accelerating Structure after a Discharge

3062

V.G. Ziemann
Uppsala University, Uppsala, Sweden

Funding: This work is supported by the 7th European Framework program EuCARD under grant number 227579.
A discharge or RF-breakdown event in a CLIC acceleration structure causes the localized release of gas molecules inside a thin conduction limited system with distributed pumping. We discuss the transient behavior of such a system in the molecular flow regime that allows an analytical solution with the help of Greens functions. They describe the temporal evolution of the gas density and the gas flow ejected from the ends of thin pipes of finite length. Distributed pumping, for example through the HOM damping slits is taken into account.

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THPME054

RF Cavity Design Aspects for a Helical Muon Beam Cooling Channel

3352

F. Marhauser, G. Flanagan, R.P. Johnson, S.A. Kahn
Muons, Inc, Illinois, USA
K. Yonehara
Fermilab, Batavia, Illinois, USA

Funding: Work supported under U.S. DOE Grant Application Number DE-SC0006266
A Helical Cooling Channel (HCC) promises efficient six-dimensional ionization cooling of muon beams by utilizing high-pressurized gas as a continuous absorber within a magnetic channel embedding RF cavities. The progress on cavity design, tailored for such a cooling channel, is discussed.

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THPRI031

Design and Commissioning of S-Band RF Station for AREAL Test Facility

3834

A. Vardanyan, H. Avdishyan, H. Davtyan, B. Grigoryan, L.H. Hakobyan, H. Poladyan
CANDLE SRI, Yerevan, Armenia

The RF station has been designed and constructed for AREAL Linac. The constructional features and commissioning results of RF system are presented. The whole RF system is designed to work at 3GHz frequency. The linac includes an electron gun for 0.5-8 ps electron bunch production with 1-10 Hz repetition rate. For linac RF control system a Libera LLRF stabilization system is used. An important feature of the presented system is a high level synchronization of amplitude-phase characteristics which provide the required accuracy for particle acceleration and bunch formation.

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THPRI032

Study of a RF Gun with a Thermoionic Cathode

3837

A.S. Setty, A.S. Chauchat, D. Fasse, D. Jousse, P. Sirot
Thales Communications & Security (TCS), Gennevilliers Cedex, France

The low energy part of our pre injectors* is made up of a 90 kV DC thermoionic triode gun, followed by a 500 MHz sub harmonic prebuncher and a 3 GHz prebuncher. These two cavities are respectively fed with 500 W, a modulation of ± 25 kV, and 90 W corresponding to a ± 10 kV. The gun grid is modulated within a 500 MHz signal. The initial 1 ns phase extension at the gun level is reduced, at the buncher entry, to 40 ps for 75% of the gun current. This study proposes to replace the gun and the two cavities by a RF gun integrated in a modulated cavity at 200 MHz followed by a drift in order to bunch the beam. This study will compare the beam dynamics simulations for these two cases.
*A. Setty et al, "Design and Construction of Turnkey Linacs as Injectors for Light Sources", Proceedings IPAC 2012, USA, Louisiana, May 2012.

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THPRI033

Design of New Buncher Cavity for Relativistic Electron Gun for Atomic Exploration – REGAE

3840

M. Fakhari, H. Delsim-Hashemi, K. Flöttmann, M. Hüning, S. Pfeiffer, H. Schlarb
DESY, Hamburg, Germany
J. Roßbach
Uni HH, Hamburg, Germany

The Relativistic Electron Gun for Atomic Exploration, REGAE, is a small electron accelerator build and operated at DESY. Its main application is to provide high quality electron bunches for time resolved diffraction experiments. The RF system of REGAE contains different parts such as low level RF, preamplifier, modulator, phase shifter, and cavities. A photocathode gun cavity to produce the electrons and a buncher cavity to compress the electron bunches in the following drift tube. Since the difference between the operating mode of the existing buncher and its adjacent mode is too small, the input power excites the other modes in addition to the operating mode which affects the beam parameters. A new buncher cavity is designed in order to improve the mode separation. Furthermore the whole cavity is modeled by a circuit which can be useful especially during the tuning process. Beam dynamics simulations have been performed in order to compare the new designed cavity with the old one which declare that the effects of the adjacent modes on the beam parameters are decreased.

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THPRI035

Design and Simulation of Side Coupled Six MeV Linac for X-Ray Cargo Inspection

3844

S. Ahmadiannamin, F. AbbasiDavani, R. Ghaderi, F. Ghasemi
sbu, Tehran, Iran
M. Lamehi Rashti
IPM, Tehran, Iran
S. Zarei
Nuclear Science and Technology Research, InstituteRadiation Application School, Tehran, Iran

Using in X-ray cargo inspection is one of most applications of linear accelerators. This paper represents design and simulation of Side Coupled Six MeV cavity. The electromagnetic simulation of structure was carried out in the SUPERFISH and CST Microwave studio. 2.3 MW input power is considered according to MG5193 magnetron. The coupling coefficient is calculated equal to 3% for stabilization of accelerator operation against environmental and mechanical errors effects.

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THPRI038

Simulation Study of Electron Gun for Six MeV Linac for X-Ray Cargo Inspection

3847

S. Ahmadiannamin, F. AbbasiDavani, R. Ghaderi, F. Ghasemi
sbu, Tehran, Iran
M. Lamehi Rashti
IPM, Tehran, Iran
S. Zarei
Nuclear Science and Technology Research, InstituteRadiation Application School, Tehran, Iran

Electron guns are designed in different models. Output beam quality and efficiency of the linear accelerator for each application depends on choosing the suitable model of electron gun. The most common types are diode and triode electron guns. Simulation Study of diode electron gun of Six MeV Linac for X-Ray Cargo Inspection represented in this article. Vaughan analytical method was used to obtain the initial dimensions. In final stage, CST Particle Studio software used to obtain the dimensional details.

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THPRI041

Twenty Years of Operation of the Elettra RF System

3853

C. P. Pasotti, M. Bocciai, P. Pittana, M. Rinaldi
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Six thousand hours per year is the typical running scheduled time of the user-dedicated Elettra facility and twenty years is a significant amount of operating hours for the RF system. Failure and weak points of the installed equipment is discussed as well as the up-time statistic. The effectiveness of the predictive versus the extraordinary maintenance is presented. The gained operational experience has allowed the planning of the priorities to refit the installed components within a reasonable budget, in compliance with the user-operation time schedule and following the technical need of upgrading to improve the RF system performance.

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THPRI042

Design and RF Test of Damped C-Band Accelerating Structures for the ELI-NP Linac

3856

D. Alesini, S. Bini, R. D. Di Raddo, V.L. Lollo, L. Pellegrino
INFN/LNF, Frascati (Roma), Italy
L. Ficcadenti, V. Pettinacci
INFN-Roma, Roma, Italy
L. Palumbo
URLS, Rome, Italy
L. Serafini
Istituto Nazionale di Fisica Nucleare, Milano, Italy

The linac energy booster of the European ELI-NP proposal foresees the use of 12 traveling wave C-Band structures, 1.8 m long with a field phase advance per cell of 2pi/3 and a repetition rate of 100 Hz. Because of the multi-bunch operation, the structures have been designed with a damping of the HOM dipoles modes in order to avoid beam break-up (BBU). They are quasi-constant gradient structures with symmetric inputs couplers and a strong damping of the HOM in each cell. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce their cost. In the paper we shortly review the whole design criteria and we illustrate the low and high power RF test results on prototypes that shown the feasibility of the structure realization and the effectiveness of the HOM damping.

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THPRI043

Thermal-mechanical Analysis of the RF Structures for the ELI-NP Proposal

3860

V. Pettinacci
INFN-Roma, Roma, Italy
D. Alesini, L. Pellegrino
INFN/LNF, Frascati (Roma), Italy
L. Palumbo
URLS, Rome, Italy

The room temperature RF structures in the ELI-NP Linac will operate in multi-bunch with high repetition rate (100 Hz). For these reasons they are subject to some kW of power dissipated on the internal cavities surfaces. The resulting thermal deformation of the cavities shapes could imply variations in their electromagnetic fields. To limit these effects and optimize the cooling design, a fully coupled ElectroMagnetic- Thermal-Mechanical analysis has been performed on the S-Band Radiofrequency Gun and on the C-Band multi-cell structures. In the paper the study done in Ansys Workbench with HFSS and Ansys Mechanical is reviewed

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THPRI044

Vacuum Waveguide System for SPring-8 Linac Injector Section

3863

T. Taniuchi, H. Dewa, H. Hanaki, T. Kobayashi, T. Magome, A. Mizuno, S. Suzuki, K. Yanagida
JASRI/SPring-8, Hyogo-ken, Japan

An SF6 waveguide system for the injector section of SPring-8 linac has been replaced in a vacuum waveguide system including a newly developed vacuum circulator and an isolator. This paper describes developed RF components, a waveguide configuration and an RF conditioning of the system.

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THPRI045

Development of a 1.3-GHz Buncher Cavity for the Compact ERL

3866

T. Takahashi, Y. Honda, T. Miura, T. Miyajima, H. Sakai, S. Sakanaka, K. Shinoe, T. Uchiyama, K. Umemori, M. Yamamoto
KEK, Ibaraki, Japan

In a high-brightness injector of the Compact ERL (cERL), a 1.3-GHz buncher cavity is used to compress the electron bunches which are produced at a 500-kV photocathode DC electron gun. An rf voltage required is about 130 kV. To elongate the lifetime of the photocathode of the DC gun which is located beside the buncher cavity, an extremely-low pressure of about 10^-9 Pa is required in the buncher cavity under operating conditions. In order to achieve such low pressures, we have developed a normal-conducting cavity which included several measures to reduce the outgas from the cavity components, together with careful rf designs to avoid any problems due to multipactor discharges or to other problems. With the developed cavity, we achieved a vacuum pressure of about 2·10^-9 Pa under rf operations at an rf voltage of about 100 kV. The buncher cavity was installed in the cERL, and it worked very well; we could demonstrate to compress the bunch length from 10 ps (FWHM) to 0.5 ps (rms) using the buncher cavity.

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THPRI046

Air-cooled Magnetic Alloy Cavity for J-PARC Doubled Rep.-rate Scenario

3869

C. Ohmori, K. Hara, K. Hasegawa, K. Takata, M. Toda, M. Yoshii
KEK, Ibaraki, Japan
M. Nomura, A. Schnase, T. Shimada, F. Tamura, M. Yamamoto
JAEA/J-PARC, Tokai-mura, Japan

The upgrade project of the J-PARC MR (Main Ring) is in progress to deliver the beam power of 750 kW based on doubled repetition-rate scenario. The present RF section will be occupied by 9 sets of new magnetic alloy, FT3L, cavity using the direct water cooling scheme. The direct water cooling requires dedicated high-quality cooling water. These cavities will be used for the fundamental RF for acceleration. The second harmonic RF is necessary to increase the bunch length. This allows to enlarge the beam current, and to relax the space charge effects during the injection. Thanks to the high impedance FT3L, the power loss in the second harmonic RF system becomes moderate. The air cooled cavity is designed to fit in any space in the MR where the dedicated water is not available. This paper reports the design of the second RF system, technical issues to produce the magnetic alloy cores to fit the air cooling, and construction of the system.

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THPRI047

Large-aperture Travelling-wave Accelerator Structure for Positron Capture of SuperKEKB Injector Linac

3872

S. Matsumoto, T. Higo, K. Kakihara, T. Kamitani, M. Tanaka
KEK, Ibaraki, Japan

Comparing to the previous KEKB, the four-times higher charge of 4 nC per bunch is required for the injector linac of SuperKEKB. Not only a flux concentrator will be introduced but also the physical aperture of the downstream six 2m-long accelerator structures was increased as large as 30mm in diameter. We call these structures as LAS, “Large Aperture S-band” structure. The resultant higher RF group velocity of about 3% makes the acceleration gradient lower. In the nominal acceleration system, a 40MW klystron with SLED feeds four 2m-long accelerator structures producing 20MV/m acceleration field. The acceleration gradient higher than 14 MV/m is required for the very first two LAS structures to suppress the satellite bunches. This gradient is obtained by feeding only two LAS structures. Initially, ten LAS structures were installed and the RF processing has partly started. In the present paper, we firstly describe the acceleration system design and then present the processing characteristics through the RF processing without beam and with beam.

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THPRI048

Design of an Accelerating Tube for a Standing-wave Accelerator based on Genetic Algorithm’s Optimal Calculation

3875

SUSPSNE090

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Z.X. Tang
USTC, Hefei, Anhui, People's Republic of China
Y.J. Pei
USTC/NSRL, Hefei, Anhui, People's Republic of China

A compact medical standing-wave (SW) electron accelerating tube has been designed that operating frequency is 2998MHz, operating mode is π/2, final energy is 6MeV and beam current is 100mA based on genetic algorithm (GA)’s optimal calculation. It employed a bi-periodic structure with nose cone shape. We performed the simulation experiment which proved that GA was feasible and gave a set of geometric parameter with higher shunt impedance. We performed tuning of the whole tube by CST MICROWAVE STUDIO and SUPERFISH and calculation of beam dynamics by ASTRA and Parmela in this paper. The total length of the tube is less than 300mm.

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THPRI049

Engineering Design of the RF Input Couplers for C-ADS RFQ

3878

L.P. Sun, Y. He, A. Shi, C. Zhang, Z.L. Zhang
IMP, Lanzhou, People's Republic of China

A new coupler with the special ceramic window has been developed at IMP, CAS (Institute of Modern Physics, Chinese Academy of Sciences), operating at 30 kW/162.5 MHz in CW mode for an one-meter prototype cavity, which can provide all kinds of experiences to the real four-meter cavity including EM simulation, power conditioning, cooling consideration and so on. Now, the beam experiments on prototype cavity have been completed and the results show the simulation and the measurements of coupler were in the good agreement. The special bowl-type ceramic window can promote S parameter and reduce sparking risk for beam commissioning stably. A detailed electromagnetic design and measured results of the coupler will be presented in the paper.

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THPRI050

Calculation and Design of the Re-buncher Cavities for the LIPAc Deuteron Accelerator

3881

D. Gavela, I. Podadera, F. Toral
CIEMAT, Madrid, Spain

Funding: This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project AIC-A-2011-0654
Two re-buncher cavities are necessary for the LIPAc (Linear IFMIF Prototype Accelerator), presently being built at Rokkasho (Japan). They are placed at the Medium Energy Beam Transport (MEBT) line to longitudinally focus a 5 MeV CW deuteron beam. Due to the strong space charge and the compactness of the beamline, the cavity has several space restrictions. In order to minimize the power loss, an IH-type cavity with 5 gaps was selected. It provides an effective voltage of 350 kV at 175 MHz with a power loss of 6.6 kW. First, electromagnetic calculations have been done with HFSS to compute the resonant frequency, the S-parameters, the electric and magnetic field maps, the power losses and the proper geometry for a magnetic input coupler and a pickup probe. Then, a mechanical Ansys model has been used to analyze the stresses and deformations due to vacuum, the cooling circuit and the temperature distribution, taking into account the power losses imported from the electromagnetic model. Finally, the fluid dynamics in the cooling circuits of the stems has been carefully studied.

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THPRI051

Fabrication and Tests of the Re-buncher Cavities for the LIPAc Deuteron Accelerator

3884

D. Gavela, P. Abramian, J. Calero, A. Guirao, J.L. Gutiérrez, E. Molina Marinas, I. Podadera, L. Sánchez, F. Toral
CIEMAT, Madrid, Spain

Funding: This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project AIC-A-2011-0654
Two re-buncher cavities will be installed at the Medium Energy Beam Transport (MEBT) of the LIPAc accelerator, presently being built at Rokkasho (Japan). They are IH-type cavities with 5 gaps and will provide an effective voltage of 350 kV at 175 MHz. The cavity consists of a cylindrical main body and two endplates in stainless steel with an internal copper coating. The stems and drift tubes are machined from bulk OFE copper. The fabrication techniques for the cooling pipes, the input coupler and the pick-up are presented. Material choices and fabrication process are discussed. The first re-buncher is already fabricated. RF low power tests have been made to measure resonant frequency, S-parameters and Q-factor before and after the copper plating. The electric field map has also been measured with the bead-pull method.

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THPRI052

Design, Fabrication and Tests of the Second Prototype of the Double-Length CLIC PETS

3887

L. Sánchez, J. Calero, D. Gavela, J.L. Gutiérrez, F. Toral
CIEMAT, Madrid, Spain
D. Gudkov, G. Riddone
CERN, Geneva, Switzerland

Funding: This work has been partially funded by the Spanish Ministry of Economy and Competitiveness under project FPA2010-21456-C02-02
The future collider CLIC is based on a two-beam acceleration scheme, where the drive beam provides to the main beam the RF power through the Power Extraction and Transfer Structures (PETS). The technical feasibility of some components is currently being proved at the CLIC Experimental Area (CLEX). Two double- length CLIC PETS will be installed in CLEX to validate their performance with beam. The first prototype was produced and validated in 2012. This paper is focused on the engineering design, fabrication and validation of the second prototype. Taking into account the results of the first prototype, some modifications have been included in the design to ease fabrication and assembly. The fabrication techniques are very similar to the ones used for the first prototype. Mechanical measurements on single parts and different assembly stages will be reported. The industrialization feasibility will be also analyzed. Finally, several tests such as vacuum tightness and RF measurements with low power have been realized to validate the device. These results are compared with the first prototype ones.

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THPRI053

Ferrite Material Characterization in a Static Bias Field for the Design of a Tunable Cavity

3890

SUSPSNE088

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J. Eberhardt, F. Caspers, C. Vollinger
CERN, Geneva, Switzerland

During the development of ferrite-loaded accelerating cavities, the electromagnetic properties of the dispersive ferrite material need to be known. We describe a coaxial short-circuit measurement technique to measure the complex permeability of toroidal-shaped samples (127mm outer and 70mm inner diameter) that are exposed to an external magnetic bias field. The external magnetic bias field is applied perpendicular to the RF magnetic field. With this method it is possible to characterize the frequency dependence of the permeability for a frequency range of 1-100MHz. The dependence of the permeability on the external magnetic bias is presented for the ferrite G-510 from Trans-Tech Inc. and the material characterization is shown in the same frequency range. The measurement results are verified by simulations of the measurement set-up.

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THPRI054

Permittivity and Permeability Measurement Methods for Particle Accelerator Related Materials

3893

C. Vollinger, F. Caspers, E. Jensen
CERN, Geneva, Switzerland

For the special requirements related to particle accelerators, knowledge of the different material parameters of dielectrics and other materials are needed in order to carry out simulations during the design process of accelerator components. This includes also properties of magnetically biased ferrites of which usually little information is available about material characteristics, especially in magnetic bias fields. Several methods of measurement are discussed and compared of which some require delicate sample preparation whereas others can work with unmodified material shapes that makes those methods also suited for acceptance checks on incoming materials delivered by industry. Applications include characterization of different materials, as absorbers in which dielectric losses play an increasing role, as well as low frequency measurements on ferrites that are used for tunable cavities. We present results obtained from both broadband and resonant measurements on different materials determined in the same sample holder. Where possible, the results were confirmed with alternative methods.

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THPRI055

The New 118 MHz Normal Conducting RF Cavity for SIAM Photon Source at SLRI

3896

N. Juntong, S. Krainara
SLRI, Nakhon Ratchasima, Thailand

The Siam Photon Source (SPS) is the 1.2 GeV second generation light source in Thailand. It is managed by the Synchrotron Light Research Institute (SLRI). The institute is located inside the campus of Suranaree University of Technology (SUT), which is approximately 20 km from the city of Nakhon Ratchasima (or normally called Korat). Korat is 250 km north-east of Bangkok. Two insertion devices (IDs) have been installed in the SPS storage ring during June to August 2013. These IDs require additional electrical field energy from RF cavity to compensate electron energy loss in the storage ring. The existing RF cavity has been pushed to its maximum capability and the new RF cavity is in the procurement process. The design and study of the new RF cavity will be presented. Electromagnetic fields of the cavity are studied together with the effects to electron beam instabilities.

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THPRI056

A New Debunching Cavity for the ISIS H⁻ Injector

3899

B.S. Drumm, A.P. Letchford, R.E. Williamson
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
M. Keelan
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom

The energy range of the ISIS 70MeV H⁻ injected beam is reduced using an RF debunching cavity. The existing cavity consists of a mild steel vacuum vessel containing a water-cooled copper shell into which RF power is fed. The unit is made up of components designed for the 50 MeV Proton Linear Accelerator (PLA) which used to occupy the Rutherford Appleton Laboratory (RAL) site between 1957 and 1969. The component drawings date back to the late 1960s. Due to its age, complexity and a lack of spares, there is a need for a modern solution. This paper documents the development of a new debunching cavity for the ISIS neutron source.

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THPRI058

RF Delivery System for FETS

3902

S.M.H. Alsari, M. Aslaninejad, J.K. Pozimski, P. Savage
Imperial College of Science and Technology, Department of Physics, London, United Kingdom
M. Dudman, A.P. Letchford
STFC/RAL, Chilton, Didcot, Oxon, United Kingdom

The Front End Test Stand (FETS) is an experiment based at the Rutherford Appleton Laboratory (RAL) in the UK. In this experiment, the first stages necessary to produce a very high quality, chopped H⁻ ion beam as required for the next generation of high power proton accelerators (HPPAs) are designed, built and tested. HPPAs with beam powers in the megawatt range have many possible applications including drivers for spallation neutron sources, neutrino factories, accelerator driven sub-critical systems, waste transmuters and tritium production facilities. An RF system outline, circulator high power tests, RF amplifiers tests, waveguide run with shielding and couplers design are presented and discussed in this paper. Experimental measurements of the system’s circulator and RF Amplifiers high power test will be presented as part of the system testing results.

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THPRI059

Field Emission Study of RF cavity in Static Magnetic Field

3905

T.H. Luo, D. Li
LBNL, Berkeley, California, USA
W. Gai
ANL, Argonne, Illinois, USA
J.H. Shao
TUB, Beijing, People's Republic of China

The RF cavity performance in solenoid magnetic field is crucial for the muon ionization cooling. Previous experiments have shown that the strong external magnetic field can significantly lower the maximum achievable RF voltage in the cavity. The mechanism of this performance degradation has been studied both analytically and experimentally, but so far no conclusive cause has been determined yet. In this paper, we propose an experiment to study the effect of a static B field on the field emission in the RF cavity, which hasn't been investigated before, and which can contribute to the cavity performance degradation in the solenoid field.

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THPRI061

Perpendicular Biased Ferrite Tuned Cavities for the Fermilab Booster

3911

G.V. Romanov, M.H. Awida, T.N. Khabiboulline, W. Pellico, C.-Y. Tan, I. Terechkine, V.P. Yakovlev, R.M. Zwaska
Fermilab, Batavia, Illinois, USA

The aging Fermilab Booster RF system needs an upgrade to support future experimental program. The important feature of the upgrade is substantial enhancement of the requirements for the accelerating cavities. The new requirements include enlargement of the cavity beam pipe aperture, increase of the cavity voltage and increase in the repetition rate. The modification of the present traditional parallel biased ferrite cavities is rather challenging. An alternative to rebuilding the present Fermilab Booster RF cavities is to design and construct new perpendicular biased RF cavities, which potentially offer a number of advantages. An evaluation and a preliminary design of the perpendicular biased ferrite tuned cavities for the Fermilab Booster upgrade is described in the paper. Also it is desirable for better Booster performance to improve the capture of beam in the Booster during injection and at the start of the ramp. One possible way to do that is to flatten the bucket by introducing second harmonic cavities into the Booster. This paper also looks into the option of using perpendicularly biased ferrite tuners for the second harmonic cavities.

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THPRI064

Plasma Chemistry in a High Pressure Gas Filled RF Test Cell for use in a Muon Cooling Channel

3917

B.T. Freemire, Y. Torun
IIT, Chicago, Illinois, USA
M. Chung, M.R. Jana, M.A. Leonova, A. Moretti, T.A. Schwarz, A.V. Tollestrup, Y. Torun, K. Yonehara
Fermilab, Batavia, Illinois, USA
R.P. Johnson
Muons, Inc, Illinois, USA

Filling an RF cavity with a high pressure gas prevents breakdown when the cavity is placed in a multi-Tesla external magnetic field. A beam of particles traversing the cavity, be it muons or protons, ionizes the gas, creating an electron-ion plasma which absorbs energy from the cavity. In order to understand the nature of this plasma loading, a variety of gas species, gas pressures, dopants, and cavity electric fields were investigated. Plasma induced energy loss, electron-ion recombination rates, ion-ion recombination rates, and electron attachment times were measured. The results for hydrogen, deuterium, helium, and nitrogen, doped with dry air will be presented.

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THPRI066

Design of a 1.3 GHz Two-cell Buncher for APEX

3924

H.J. Qian, K.M. Baptiste, J.A. Doyle, D. Filippetto, S. Kwiatkowski, C. F. Papadopoulos, D. Patino, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA

Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The design of a 1.3 GHz buncher cavity for the APEX project, a MHz repetition rate high-brightness photoinjector, is presented. The buncher cavity operates at 240 kV in CW mode, and it compresses the 750 keV beam from APEX gun through ballistic compression. Compared with a single cell design, a two-cell cavity doubles the shunt impedance to 7.8 MΩ, which greatly relaxes the requirements for both RF amplifier and cavity cooling. Coupler design, multipacting analysis, HOM analysis and thermal analysis will be presented in this paper.

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THPRI070

Tuner System Simulation and Tests for the 201-MHz MICE Cavity

3927

L. Somaschini
INFN-Pisa, Pisa, Italy
A.J. DeMello, A.R. Lambert, S.P. Virostek
LBNL, Berkeley, California, USA
J.H. Gaynier, R.J. Pasquinelli, D.W. Peterson, R.P. Schultz
Fermilab, Batavia, Illinois, USA
Y. Torun
Illinois Institute of Technology, Chicago, Illlinois, USA

Funding: Supported by the US Department of Energy Office of Science through the Muon Accelerator Program.
The frequency of MICE cavities is controlled by pneumatic tuners as their operation is impervious to large magnetic fields. The mechanical and RF transfer functions of the tuner were simulated in ANSYS. The first of these tuning systems was assembled and tested at Fermilab. The mechanical response and the RF tuning transfer function have been measured and compared with simulation results. Finally the failure of different actuators has been simulated and tested to predict the operational limits of the tuner.

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THPRI073

Achieving Higher Energies via Passively Driven X-band Structures

3933

SUSPSNE089

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T. Sipahi, S. Biedron, S.V. Milton
CSU, Fort Collins, Colorado, USA

Due to their higher intrinsic shunt impedance X-band accelerating structures significant gradients with relatively modest input powers, and this can lead to more compact particle accelerators. At the Colorado State University Accelerator Laboratory (CSUAL) we would like to adapt this technology to our 1.3 GHz L-band accelerator system using a passively driven 11.7 GHz traveling wave X-band configuration that capitalizes on the high shunt impedances achievable in X-band accelerating structures in order to increase our overall beam energy in a manner that does not require investment in an expensive, custom, high-power X-band klystron system. Here we provide the design details of the X-band structures that will allow us to achieve our goal of reaching the maximum practical net potential across the X-band accelerating structure while driven solely by the beam from the L-band system.

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THPRI075

S-Band Structure Study for the MaRIE Project

3940

Z. Li, C. Adolphsen, M.V. Fazio, S.G. Tantawi, L. Xiao
SLAC, Menlo Park, California, USA

Funding: Work was supported by the US Department of Energy through the LANL/LDRD Program.
The Matter-Radiation Interactions in Extremes (MaRIE) facility proposed at LANL utilizes a 20-GeV electron linac to drive a 50-keV XFEL. Experimental requirements drive a need for multiple photon bunches over time durations of about 10 microsecond produced by a bunch train of interleaving 0.1 nC very low-emittance bunches with 2-nC electron bunches. The linac is required not only to provide high gradient and high efficient acceleration, but also a controlled wakefield profile to maintain the beam quality. In this paper, we explore the feasibility of using the S-Band technology to meet such acceleration requirements. We will present the design optimization and comparison of S-Band structures based on different design considerations.

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THPRI076

Laser Triggered RF Breakdown Study Using an S-band Photocathode Gun

3943

J.H. Shao, W. Gai
ANL, Argonne, Illinois, USA
H.B. Chen, Y.-C. Du, W.-H. Huang, J. Shi, C.-X. Tang, L.X. Yan
TUB, Beijing, People's Republic of China
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
F.Y. Wang
SLAC, Menlo Park, California, USA

A laser triggered RF breakdown experiment was carried out with an S-band photocathode gun at Tsinghua University for attempting understanding of the RF breakdown processes. By systematic measurement of the time dependence of the breakdown current at the gun exit and the stored RF energy in the cavity, one might gain insight into the time evolution of RF breakdown physics. A correlation of the stored energy and field emission current has been analysed with an equivalent circuit model. Experimental details and analysis methods are reported.

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THPRI077

Electric Field Enhancement Study using an L-band Photocathode Gun

3946

J.H. Shao, W. Gai
ANL, Argonne, Illinois, USA
H.B. Chen, J. Shi
TUB, Beijing, People's Republic of China
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
F.Y. Wang, L. Xiao
SLAC, Menlo Park, California, USA

RF breakdown in high gradient accelerating structures is a fundamental problem that is still needed better understanding. Past studies have indicated that field emission, which is usually represented by electric field enhancement (i.e. β) produced from the Fowler-Nordheim plot, is strongly coupled to the breakdown problem. A controlled surface study using a high gradient L-band RF gun is being carried out. With a flat cathode, the maximum electric field on the surface reached 10³ MV/m. And electric field as high as 565 MV/m on the surface was achieved by a pin-shaped cathode. The field enhancement factor was measured at different surface field during the conditioning process. Initial results of the study are presented in this paper.

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THPRI078

Experimental Study of Surface RF Magnetic Field Enhancement Caused by Closely Spaced Protrusions

3949

F.Y. Wang, C. Adolphsen, J.P. Eichner, C.D. Nantista, L. Xiao
SLAC, Menlo Park, California, USA

The RF magnetic field enhancement between two closely spaced protrusions on a metallic surface has been studied theoretically. It is found that a large enhancement occurs when the field is perpendicular to the gap between the protrusions. This mechanism could help explain the melting that has been observed on cavity surfaces subjected to pulsed heating that would nominally be well below the melting temperature of the surface material. To test this possibility, an experiment was carried out in which a pair of copper “pins” was attached to the base plate of an X-band cavity normally used to study pulsed heating. Melting was observed between the pins when the predicted peak temperature was near or exceeded the copper melting temperature.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI078

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THPRI080

The New Design for Capture Cavity of CEBAF

3955

S. Wang, J. Guo, R.A. Rimmer, H. Wang
JLab, Newport News, Virginia, USA

In CEBAF, the electron beam from the injector must be sufficiently relativistic to match a 1 GeV recirculated beam in the first linac. The electron beam is produced with a ~130 keV electron gun, then accelerated by a room temperature, graded-beta standing wave linac, capture section, from 130 keV to 510 keV before enters two 5-cell superconducting RF cavities for further acceleration. Present capture cavity is a 5-cell side-coupled cavity. We designed a new slot-coupled cavity which has lower power consumption and simpler structure.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI080

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)